CAMBRIDGE, Mass., June 18, 2007 - Genzyme Corp. (Nasdaq: GENZ)
today announced the results of two new studies comparing a powder
form of Renvela™ (sevelamer carbonate) to Renagel®
tablets (sevelamer hydrochloride), including one trial in which
patients received the powder form three times per day, and one in
which it was administered once per day.

Genzyme is developing Renvela in powder form to provide an
additional option for patients with chronic kidney disease in
managing their phosphate levels. A New Drug Application for Renvela
tablets is already on file with the FDA, and previous studies have
shown that the tablet formulation provides equivalent phosphate
control to Renagel in patients on dialysis and significant
phosphorus control in patients with chronic kidney disease who are
not on dialysis. Today’s results are the first from trials
comparing the efficacy of the powder form of Renvela to Renagel
tablets.

In the first powder trial, patients treated with the powder form
of Renvela three times per day experienced equivalent phosphorus
control to patients treated with Renagel tablets three times per
day. As a result, this trial successfully met its primary
endpoint.

In the second trial, patients dosed with the powder form of
Renvela once per day and those treated with Renagel tablets three
times per day achieved statistically significant reductions in
serum phosphorus, with both groups reaching target levels for
phosphorus control outlined in the K/DOQI treatment guidelines.
Phosphorus levels in the Renagel arm (4.6 mg/dL) were lower than
those in the Renvela arm (5.3 mg/dL), and this trial did not
achieve its primary endpoint of demonstrating non-inferiority of
Renvela powder dosed once per day to Renagel tablets dosed three
times per day.

In both trials, the safety profile of Renvela was consistent
with the previous clinical experience of patients on dialysis using
Renagel.

With today’s results, Genzyme has concluded that the
powder formulation of Renvela dosed three times per day may
represent a promising alternative for patients with chronic kidney
disease. The company will continue to move ahead aggressively with
clinical and regulatory plans for the powder formulation dosed
three times per day, and these data will form part of an NDA
submission in the first half of 2008.

“We are very pleased with the progress we have made to
date in our multi-faceted development program for Renvela,
including filing an NDA for patients on dialysis, completing a
successful trial in the pre-dialysis population, and demonstrating
the effectiveness of the powder formulation dosed three times per
day,” said John P. Butler, president, Genzyme Renal.
“Results of the once-per-day trial were greatly influenced by
the strong phosphorus reduction seen in the Renagel arm, which was
superior to that seen in all but one previously conducted clinical
trials. While today’s results will not currently support a
regulatory filing for once-per-day dosing, they are clinically
meaningful and give us confidence that this approach can be
effective. We will continue to work with regulatory authorities to
design an appropriate clinical plan to gain approval for this
dosing regimen.”

About Renvela

Renvela is a buffered form of Renagel, the most-prescribed
phosphate binder in the United States. Like Renagel, Renvela is a
calcium-free, metal-free, non-absorbed phosphate binder, and will
be available as 800mg tablets once approved. A New Drug Application
for Renvela is currently under review by the US Food and Drug
Administration for the control of serum phosphorus in patients with
chronic kidney disease on dialysis.

In April, Genzyme announced that a new clinical trial showed
that Renvela significantly reduced serum phosphorus,
calcium-phosphorus product and LDL cholesterol in hyperphosphatemic
patients with chronic kidney disease who are not on dialysis.
Additionally, data showing the equivalence of sevelamer carbonate
and sevelamer hydrochloride were presented at the 2007 spring
clinical meeting of the National Kidney Foundation.

About Renagel

Renagel controls serum phosphorus in patients with CKD on
hemodialysis. Controlling serum phosphorus is an important element
in the care of hemodialysis patients. Elevated serum phosphorus
levels are common in dialysis patients and associated with
increased risk of cardiovascular mortality. Renagel provides the
added benefit of significant LDL cholesterol reduction (32
percent).

The National Kidney Foundation’s 2003 K/DOQI guidelines
for Bone Metabolism and Disease in Chronic Kidney Disease recommend
sevelamer hydrochloride as a first-line treatment option to control
phosphorus. Renagel is the only phosphate binder available that
does not contain either calcium or a metal. It has an established
safety profile, is not systemically absorbed and provides
phosphorus control without the concerns of calcium or metal
accumulation. Renagel is used by more than 350,000 people
worldwide.

Renagel is indicated for the control of serum phosphorus in
patients with chronic kidney disease (CKD) on hemodialysis.
Renagel is contraindicated in patients with hypophosphatemia
or bowel obstruction. In a 52-week study, the most common
side effects included vomiting, nausea, diarrhea, and dyspepsia.
Drug-drug interactions may occur with some medications and
should be taken into consideration when instructing patients how to
take Renagel.

For more information about Renagel, including complete
prescribing information, please visit www.renagel.com.

About Genzyme

One of the world's leading biotechnology companies, Genzyme is
dedicated to making a major positive impact on the lives of people
with serious diseases. Since 1981, the company has grown from a
small start-up to a diversified enterprise with more than 9,000
employees in locations spanning the globe and 2006 revenues of $3.2
billion. Genzyme has been selected by FORTUNE as one of the
“100 Best Companies to Work for” in the United
States.

With many established products and services helping patients in
nearly 90 countries, Genzyme is a leader in the effort to develop
and apply the most advanced technologies in the life sciences. The
company's products and services are focused on rare inherited
disorders, kidney disease, orthopaedics, cancer, transplant, and
diagnostic testing. Genzyme's commitment to innovation continues
today with a substantial development program focused on these
fields, as well as immune disease, infectious disease, and other
areas of unmet medical need.

Genzyme® and Renagel® are registered trademarks and
RenvelaTM is a trademark of Genzyme Corporation. All rights
reserved.

This press release contains forward-looking statements
including, without limitation, statements about the development of
Renvela™ for chronic kidney disease and alternative dosing
regimens for the powder formulation of Renvela™. These
statements are subject to risks and uncertainties that could cause
actual results to differ materially from those projected in these
forward-looking statements. These risks and uncertainties include,
among others: additional analysis of the data comparing the powder
form of Renvela™ to Renagel®; the results of other
studies and whether such results are consistent with this data; the
actual efficacy and safety of Renvela™ for chronic kidney
disease; the outcome of discussions with regulatory authorities
regarding clinical studies and the approval of Renvela™ for
chronic kidney disease and the timing of such discussions; the
timing and content of submissions to and decisions made by
regulatory authorities; the availability and extent of third-party
reimbursement for Renvela™; and the risks and uncertainties
described in reports filed by Genzyme with the Securities and
Exchange Commission under the Securities Exchange Act of 1934, as
amended, including without limitation the information under the
heading "Risk Factors" in the Management's Discussion and Analysis
of Financial Condition and Results of Operations section in
Genzyme’s Quarterly Report on Form 10-Q for the period ended
March 31, 2007. Genzyme cautions investors not to place substantial
reliance on the forward-looking statements contained in this press
release. These statements speak only as of the date of this press
release, and Genzyme undertakes no obligation to update or revise
these statements.

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